Surface replacement implant for the distal humerus

ABSTRACT

The present invention relates to a partial joint replacement (1000), encompassing a shell-like segment (100) with a concave inner contour (3) for the arrangement on at the bone structure of a patient, wherein the segment (100) comprises a lateral section (5) and a medial section (7) along a longitudinal direction (x), and wherein the outer contour (1) of the segment (100) comprise in longitudinal direction (x) at least one inflection point (9).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/561,430, filed Sep. 25, 2017, which is a National Stage ofInternational Application No. PCT/EP2016/056450, filed Mar. 23, 2016,the contents of both which are incorporated herein by reference in theirentirety.

The present invention relates to a medical apparatus or to a medicalsurface replacement implant according to claim 1, in particular designedas an elbow joint replacement, partial elbow joint replacement, elbowjoint implant, total joint replacement or total elbow joint replacement.The present invention further relates to a set according to claim 25 anda method according to claim 26.

Joints are subject to wear, which can affect the cartilage of the jointas well as the joint-adjacent parts of the bone. If cartilage and/orjoint are excessively damaged, which may also be due to or resultingfrom fractures, a joint replacement may be required. The damagedarticular cartilage and possibly also parts of the bone are removedwhere necessary. A joint replacement, usually made of metal, is insertedinto the joint and assumes as much as possible the function of thedamaged structures, i.e. cartilage and bone.

The object of the present invention is to provide a joint replacement ora surface replacement implant, in particular for the elbow joint withthe distal humerus and the proximal radius. Furthermore, a set and amethod are to be provided.

The object according to the present invention is achieved by an elbowjoint replacement having the features of claim 1. It is further achievedby a set having the features of the claim 25 and by a method having thefeatures of claim 26.

In particular, a partial elbow joint replacement is proposed by thepresent invention.

The elbow joint replacement comprises at least one segment, or exactlyone segment, in particular a shell-like segment, dome-like segment or adifferently curved segment, having an inner contour which is completely,or at least in section thereof, concave. The segment is configured orprovided in order to be arranged on or at at least one cartilagestructure and/or bone structure of a patient's joint.

The segment, herein referred to purely by way of example as shell-like,comprises a lateral section and a medial section (or a first section anda second section, wherein the first section lies laterally to the secondsection after implanting the elbow joint replacement). Both sections arearranged adjacent to each other (with or without contacting one anotheror being in an indirect or direct transition) along a longitudinaldirection of the shell-like segment.

An outer contour of the segment comprises in longitudinal direction ofthe elbow joint replacement or of the segment at least one or exactlyone inflection point. The inflection point is respectively optional. Itdoes not limit the scope of the present invention.

The set according to the present invention encompasses at least oneelbow joint replacement according to the present invention.

It further encompasses at least one tool for processing the bonestructure. The tool is preferably designed or configured to adapt thebone structure to an inner contour of the elbow joint replacement.

The tool (or instrument) may be a milling tool, a grater, a shaver oranother tool, in particular a cutting tool.

“Processing” of bone structures may be understood as milling, grating,removing, etc. preparing and/or adapting.

The set according to the present invention serves the processing ofcartilage structures and/or bone structures for the preparation of animplantation of, in particular a partial elbow joint replacementaccording to the present invention.

It encompasses inserting a wire, like a drill wire, a K-wire or aKirschner-wire into the bone in the joint region.

It further encompasses inserting a tool for the processing of the bonestructure using the wire. The tool can therefore be threaded through thewire.

Finally, the set according to the present invention encompasses removingthe tool from the joint region after the processing.

In all of the embodiments herein, the use of the expression “may be” and“may have” etc. is synonymous to “is preferably” or “has preferably,”etc. respectively, and is intended to illustrate an embodiment accordingto the present invention.

Whenever numerical words are mentioned herein, the person skilled in theart will comprehend them as indications of numerical lower limits.Unless it leads the person skilled in the art to an evidentcontradiction, the person skilled in the art will comprehend thespecification for example of “one” as encompassing “at least one”. Thisunderstanding is also equally encompassed by the present invention asthe interpretation that a numeric word, for example, “one” mayalternatively mean “exactly one”, wherever this is evidently technicallypossible for the person skilled in the art. Both are encompassed by thepresent invention and applies herein to all used numerical words.

Advantageous developments of the present invention are eachsubject-matter of the dependent claims and embodiments as well as of thefigures.

When an elbow joint replacement is mentioned herein, it is not intendedto be limiting. In some embodiments according to the present invention,the implant is namely configured or designed to be used as an elbowjoint replacement. In other embodiments according to the presentinvention, the implant is however configured or designed to be used forother joints than the elbow joint.

Arranging the segment on or at at least one bone structure of thepatient may take place indirectly (if there are remains of residualcartilage) or directly (without cartilage remains).

In some exemplary embodiments according to the present invention, thesubject-matters according to the present invention comprise one orseveral of the herein described features in any combination, unless sucha combination is recognized by the person skilled in the art astechnically impossible.

In some exemplary embodiments according to the present invention, aninflection point of the elbow joint is understood to be a point of theelbow joint (approximately on its outer surface or outer contour), atwhich the course of the outer contour (for example, when viewing theelbow joint replacement in a longitudinal section or from the side)changes or at which another graph associated with the elbow jointreplacement changes its curvature characteristic: The course or thegraph changes here either from right into a left curve or vice versa.

In some exemplary embodiments according to the present invention, theinflection point is to be understood in accordance with its meaning inthe context of the mathematical curve discussion.

In some exemplary embodiments according to the present invention, theinflection point is that point on the outer contour or on the graph atwhich the curvature of the outer contour or the graph changes its sign.

In some exemplary embodiments according to the present invention, theinflection point is that point at which the curvature of the outercontour or of the graph changes from concave to convex.

In some exemplary embodiments according to the present invention, theinflection point lies in a transition region between the lateral sectionand the medial section.

According to the present invention, a partial elbow joint replacement iswhen only a part or a side (lateral, medial, proximal, distal) of a boneassociated with the joint is replaced. If for example only a part or aside of the elbow joint is worn or damaged, it may suffice to renew onlythe worn or damaged part of the joint. If this is the case, then only apartial joint replacement or a one-sided surface replacement ismentioned. Only a part of the end of the bone associated with the joint,such as the humerus, is replaced; the joint replacement does not affectthe entire medial-lateral extent of the bone, such as the humerus. Thejoint replacement may have a less longitudinal extension than the jointsurface. The longitudinal extension may be less than the width of thebone.

A total joint replacement is mentioned by the present invention when thedistal humerus, in particular only the complete surface of the capitulumwithout trochlea, and the proximal radius or radial head is replaced byimplants.

Furthermore, a joint replacement may be mentioned by the presentinvention when previously implanted implants of the distal humerusand/or of the proximal radius are replaced by other or further or newimplants.

In some exemplary embodiments according to the present invention, theterms “lateral” and “medial” refer to the placement of the elbow jointreplacement on the patient in the implanted condition as intended.“Lateral” and “medial” are understood as one understands these terms inrelation to the patient.

In some exemplary embodiments according to the present invention, theinner contour of the segment is the inner side, or concave side, or theside facing the bone or contacting it after implantation indirectly ordirectly.

In some exemplary embodiments according to the present invention, thesurface facing the joint surface during use of joint replacement, apolished, abrasion-proof and thus tribologically-optimized surface.

In some exemplary embodiments according to the present invention, theinner side, facing the bone during use of the joint replacement,comprises material characteristics and/or surface characteristics whichare regarded as osteoinductive/osteointegrative by the person skilled inthe art. The osteoinductivity may be achieved or obtained or promoted bya micro-macrostructure and/or interconnecting macrostructure, forexample by a suitable selection of surface material.

In some exemplary embodiments according to the present invention, afixed connection is provided between the treated bone bearing and theimplant during use of the joint replacement. This may be achievedthrough different anchoring principles, for example by mandrel, comb,screw connection, angularly stable screw connection. In addition, theconnection may be biologically promoted by an interaction between thebone and the implant, which gradually develops and may promote long-termstability.

In some exemplary embodiments according to the present invention, thejoint replacement comprises resorbable materials, in particular facingthe bone bearing, that degrades after implantation of the jointreplacement and which promotes stability.

In some exemplary embodiments according to the present invention, thejoint replacement or the segment is made of a biocompatible metal alloy(CoCr-alloy or the like).

In some exemplary embodiments according to the present invention, thematerial is a biocompatible metal, a ceramic, a plastic or a combinationthereof.

In some exemplary embodiments according to the present invention, themetal is CoCrMo— alloy, and/or a ceramic e.g. a zirconium oxide or analuminum oxide (Al₂O₃).

In some exemplary embodiments according to the present invention, theplastic is PEEK and/or UHMWPE (ultrahigh molecular weight polyethylene).The plastics, in particular PEEK, may be fiber-reinforced, for examplethrough carbon fibers and/or glass fibers.

In certain exemplary embodiments according to the present invention, thematerial is a carbon fiber-reinforced plastic (in short: CFP)

In some exemplary embodiments according to the present invention, theelbow joint replacement on the side of the humerus and a jointreplacement on the side of the radius form a slide pairing.

In some exemplary embodiments according to the present invention,metal-plastic or ceramic-ceramic is provided for the joint replacementas material pairing or slide pairing. This advantageously contributes tothe reduction, prevention or avoidance of abrasion when using the jointreplacement. This may also contribute to the longevity of the elbowjoint replacement, the reduction of infection risk or occurrence ofallergic reactions by the patient.

In some exemplary embodiments according to the present invention, thejoint replacement or a part thereof is designed to serve as partialor—preferably—total replacement of the radial head (caput radii). Toobtain the desired joint mechanics, sizes and proportions are basedpreferably on anatomical analysis.

In some exemplary embodiments according to the present invention, thejoint replacement comprises a plate shape or a wheel shape, for examplewhen viewing the joint replacement from the side.

In some exemplary embodiments according to the present invention, thejoint replacement comprises at least one or exactly one indentation orrecess depth on its surface or outer contour, in particular on an uppersurface thereof.

The indentation or recess depth is preferably adapted to the diameterand/or the height of the head (varies with implant sizes).

In some exemplary embodiments according to the present invention, theouter wall of the head of the joint replacement is curved. Thisadvantageously enables the joint replacement to fit into or on thejoints surface of the ulna.

In some exemplary embodiments according to the present invention, thejoint replacement comprises a coating, preferably for promotingosteointegration, on the part facing the bone. The coating may beapplied by pure titanium—plasma spray with a layer thickness of 40-50 μmand a roughness of about 7 μm. The coating may be hydroxyapatite (=bonecement) or the like. The coating may be applied on all embodimentsaccording to the present invention, for example on the distal humerus(capitulum implant) or on the proximal radius (radial head implant).

In some exemplary embodiments according to the present invention, thejoint replacement comprises an anchoring device.

In some exemplary embodiments according to the present invention, theanchoring device of the joint replacement comprises, in particular atthe proximal radius, at least one tip or at least one end section whichlies most distal after implantation. The tip or end section may berounded, which counteracts undesirable damage to the bone (e.g. theradius) during implantation and particularly during insertion.

In some exemplary embodiments according to the present invention, theanchoring device of the joint replacement comprises, in particular atthe distal humerus, at least one tip or at least one end section whichlies most proximal after implantation. The tip or end section may berounded, which counteracts undesirable damage to the bone (e.g. thehumerus) during implantation and particularly during insertion.

In some exemplary embodiments according to the present invention, theanchoring device of the joint replacement comprises lateral indentationsfor promoting osseointegration. They enable the bone to grow into them,making the implantation more stable by forming undercuts.

In some exemplary embodiments according to the present invention, theanchoring device is designed as tapered shaft, trapezoidal shaft, wedge,barb screw fixation or the like.

In some exemplary embodiments according to the present invention, theanchoring device is embodied as a plurality of flexible, elastic orbendable spikes, preferably with a re-set or restore property. Thisenables the spikes to adapt to the geometry or the surface uponinsertion into the medullary space. They are bent to the inside or theybend to the inside during implantation. By pushing against the bone tothe outside due to their flexibility and due to the stress caused bytheir bending, they contribute to the stability of the anchoring.

In some exemplary embodiments according to the present invention, thespikes or the tips comprise barbs that bury themselves into the bone,which may additionally protect against undesired translation in theaxial or radial direction, or generally against a position change, andagainst an undesirable rotation.

In some exemplary embodiments according to the present invention, thejoint replacement comprises a wedge denoted herein as short wedge.Although the greatest contribution to stability is caused or achieved byresting the head of the joint replacement on the cortical portion of theradial neck, the short wedge is inserted into the spongy bone or, ifstill present, in the medullary space to increase the stability. Due tothe little height of the wedge, the joint needs to be spread onlyslightly for implantation, which may serve to preserve the softparts/ligaments and help maintain the natural joint stability.

The wedge may have holes or openings which may be used for the ingrowthof the bone and thus for the long-term stability of the implant.

The wedge may have a T-shape in the cross section. This enables highstability of the component. In addition, it may enable a filigreedesign.

The lateral side of the wedge may be rounded to the inside. Hence, theimplant may—without or with only little spreading of the joint and/orstretching the joint line—be inserted.

The medial side of the wedge may be wider compared to the lateral side.It may be rounded. Therefore, the greatest possible contact area withthe bone may be achieved.

The rounding of the tip of the wedge may advantageously contribute tothe fact that the tip does not undesirably cut the bone and the bone isnot additionally damaged. A plateau is provided facing the head so thatthe wedge may be supported on both sides on the bone.

The wedge may have a height of 10 to 20 mm, preferably a height of about15 mm (possibly variable with different head sizes).

In some exemplary embodiments according to the present invention, thejoint replacement comprises materials which include the so-called ShapeMemory Alloys (in short: SMA), or memory metal, such as e.g. Nitinol (inshort: NiTi), cobalt chromium, composites, X-ray transparent materialsand/or ceramic.

In some exemplary embodiments according to the present invention, thejoint replacement is machined and/or produced by a casting, forming oradditive process.

The implant form may be cylindrical (advantageous because therethroughone has a simpler bone bearing processing and the implant may beinserted) to the direction of the bone (implant inner contour),triangular (see the following elaborations related thereto), cylindricalwith a medially or laterally conical course (advantageous, as there isno translation in direction of the implant's longitudinal axis). But itmay also have a barrel shape or a form adapted to the joint surface(advantageous by under cutting).

In some exemplary embodiments according to the present invention, theextension of the lateral portion (or of at least portion thereof or allportions thereof) in the radial direction is greater than the extensionof the medial portion (or of at least a portion or all portions thereof)in the radial direction. Likewise, the extension of the lateral portion(or at least a partial portion or all partial portions thereof) in theradial direction may be designed to be initially smaller, thenincreasingly larger up to an apex point, and then again flatly smaller.

In some exemplary embodiments according to the present invention, theshell-like segment comprises no closed circumference in thecircumferential direction of the segment. The circumferential directionis perpendicular to the longitudinal direction and/or perpendicular tothe radial direction of the segment.

In some exemplary embodiments of the implant of the distal humerusaccording to the present invention, the thickness of the wall of theshell-like segment is between 1 mm and 5 mm, in particular between 2 mmand 3 mm. Preferably, this applies to each wall section; preferably, nowall section in such embodiments is thicker than indicated supra.

In some exemplary embodiments according to the present invention, thesegment comprises, at least in sections thereof, an outer contour and/oran inner contour which has been adapted to be patient-specific in apreoperative planning stage via a computer imaging. In some exemplaryembodiments according to the present invention, the outer contour ispreferably such that it is identical or modeled to the congenital courseof a corresponding bone part of an elbow joint of a patient.

In some exemplary embodiments according to the present invention, theshell-like segment comprises a rough inner contour surface. Preferably,the surface roughness is an average roughness R_(a) of about 7 μm. Suchroughness, as well as macroscopic surface characteristics such as e.g.interconnecting surface structure, may contribute or lead to improvedosteointegration.

In some exemplary embodiments according to the present invention, theinner contour of the segment is designed, corresponds to or extends inthe longitudinal direction analogously to the outer contour of thesegment.

In some exemplary embodiments according to the present invention, theinner contour of the segment comprises in the longitudinal direction atleast one inflection point.

In some exemplary embodiments according to the present invention, theinner contour of the lateral section of the segment comprises a concave,non-cylindrical contour. The inner contour of the medial section of thesegment comprises a cylindrical contour in longitudinal direction.

In some exemplary embodiments according to the present invention, theinner contour of the lateral section of the segment comprises a concave,non-cylindrical contour. The inner contour of the medial section of thesegment comprises a convex contour curved to the inside in longitudinaldirection.

In some exemplary embodiments according to the present invention, theinner contour of the lateral section of the segment comprises a concave,non-cylindrical contour. The inner contour of the medial section of thesegment comprises a contour curved to the inside in longitudinaldirection.

In some exemplary embodiments according to the present invention, theinner contour of the lateral section of the segment comprises acylindrical contour and the inner contour of the medial section of thesegment comprises a convex contour in longitudinal direction or a convexcontour in circumferential direction.

In some exemplary embodiments according to the present invention, theshell-like segment comprises at its lateral end-face section a fixingunit which is configured or designed to fix the shell-like segment on orto the bone via said fixing unit.

In some exemplary embodiments according to the present invention, thefixing unit comprises, or consists of, one or at least one screw.

The shell-like segment may comprise a through-opening provided for theinsertion of the screw or a thread for fixation on the bone.

The shell-like segment may comprise a through-opening provided for theinsertion of a thread for fixation of tendons, ligaments or other tissuestructures.

In some exemplary embodiments according to the present invention, thefixing unit comprises—of each—, or consists of, at least one tab, oneweb and/or one strut or the like as a screw holder.

In some exemplary embodiments according to the present invention, thefixing unit is fixable or provided to be fixable in the bone inlongitudinal direction, parallel or substantially parallel to thelongitudinal direction.

In some exemplary embodiments according to the present invention, thesegment or sections thereof are made of a—preferablybiocompatible—metallic and/or a ceramic material and/or a compositematerial and/or polymer material (e.g. PEEK (polyetheretherketone).

In some exemplary embodiments according to the present invention, thesegment comprises at its inner side at least one fixing element foranchoring the elbow joint replacement in a bone structure.

In some exemplary embodiments according to the present invention, theinner side is the inner surface of the segment, in particular of theimplant of the distal humerus.

In some exemplary embodiments according to the present invention, thelongitudinal axis extends parallel to an axis of rotation of the elbowjoint; in the implanted condition of the elbow joint replacement, it isan axis of rotation of the elbow joint.

In some exemplary embodiments according to the present invention, theouter side of a further segment is shaped such that it is conformal orcongruent to a surface of a proximal ulna of the elbow joint.

In some exemplary embodiments according to the present invention, theelbow joint replacement ends laterally with an inlet or entrance oropening plane or wall which lies in a plane at an angle relative to thelongitudinal axis of the elbow joint replacement.

In some exemplary embodiments according to the present invention, theangle is in a range from 25° to 45°, preferably between 30° and 40°, andis particularly preferably 35°, preferably exactly or approximately 35°.

In some exemplary embodiments according to the present invention, theelbow joint replacement further encompasses a radial prosthesis orpartial radial prosthesis, in particular for the radial head (as aradial head implant) or parts thereof. This may comprise an anchoringdevice and/or a coating.

In some exemplary embodiments according to the present invention, themethod further encompasses inserting the partial elbow joint replacementwith the aid of a wire, a K-wire (the K-wire may be referred to asKirschner wire) or a drill wire, herein referred to in short as wire.

The wire is inserted preferably laterally into the axis of rotation orinto a rotation section of the implant of the distal humerus, preferablyguided as closely and as parallel to the axis of rotation as possible.

A tool, such as a miller or a shaver, is pushed by the wire and slidover the surface of the bone which is to be processed with the tool.

The tool has a tissue protector which, in use, lies between soft tissueor tissue which is not to be treated with the tool, and the bone to beprocessed.

The tool also preferably has a rotating tool section whose outer contouris either spherical, or again preferably congruent with the outercontour of the bone which is to be obtained using the tool. The rotationaxis of the tool is preferably parallel to the rotation axis of thejoint during use.

The tool or a holder for the tool may have a through-opening for theinsertion of the aforementioned wire. The tool may then be moved aroundthe axis of rotation in a controlled manner. The bone is removed by thismovement.

According to the present invention, the aforementioned tool may be usedalone. However, the present invention also encompasses two ormulti-stage processes or procedures in which, for example, a cylindricalmiller is inserted, e.g. first a cylindrical miller is introduced, e.g.via the wire as described above. Subsequently, the individual, in anycase non-cylindrical miller, may be inserted giving the bone the desirednon-cylindrical outer contour. Such a multi-stage process requires acomparatively low working height for the tool in the joint region. Thejoint line needs less expanding than in the process described above, inwhich exactly one tool is used. This may imply a preservation of thesoft tissue parts.

In some exemplary embodiments according to the present invention, themethod further encompasses removing the drill wire and optionallyinserting a fixing element for anchoring the elbow joint replacementinto the bone structure.

In some exemplary embodiments according to the present invention, theelbow joint replacement comprises a longitudinal direction, a crosssection and a circumferential direction.

In some exemplary embodiments according to the present invention, theelbow joint replacement comprises two medial or lateral ends or medialor lateral end regions which terminate in the longitudinal direction ofthe elbow joint replacement. It further comprises at least one orexactly one curved section which is curved in the circumferentialdirection of the elbow joint replacement. Alternatively, the elbow jointreplacement consists of the section which is curved in thecircumferential direction of the elbow joint replacement. The curvedsection may be the above-mentioned segment of the elbow jointreplacement.

In some exemplary embodiments according to the present invention, thecurved section is exclusively curved, e.g. exclusively convex orexclusively concave.

In some exemplary embodiments according to the present invention, theelbow joint replacement comprises the smallest curvature in a middleregion in the longitudinal direction of the elbow joint replacement.

In some exemplary embodiments according to the present invention, thecurved section comprises its greatest thickness in a middle region inthe longitudinal direction of the elbow joint replacement.

In some exemplary embodiments according to the present invention, theelbow joint replacement comprises a collar section which is medial tothe curved section.

In some exemplary embodiments according to the present invention, theinner side and/or the outer side of the collar section is medially widerthan the lateral, or wherein the inner side and/or the outer sidedecreases along the longitudinal axis from medial to lateral.

In some exemplary embodiments according to the present invention, thejoint replacement terminates medially and/or laterally with anentrance/opening plane or wall being perpendicular to the longitudinalaxis.

In some exemplary embodiments according to the present invention, theelbow replacement or the curved section comprise an upper side and abottom side in the longitudinal direction of the joint replacement, andwherein the upper side of the joint replacement and/or the curvedsection is longer than its bottom side.

In some exemplary embodiments according to the present invention, thecurved section is formed on its inner side such that it conforms to acapitulum surface of a distal humerus of the elbow joint, and/or to anolecranon fossa of a rear surface of distal humerus of an elbow joint oris congruent with it.

In some exemplary embodiments according to the present invention, thecurved section is formed at its inner side such that it conforms to, orcongruent with, another distal humeral joint surface, particularly themedial region beyond the capillary of the humerus of the elbow joint.

In certain exemplary embodiments according to the present invention, theelbow joint replacement is completely or partially prepared orconfigured to be fixed in the bone structures using bone cement. Inthis, the surfaces of the implants, or sections thereof, may be coatedor not coated, surface-treated or not surface-treated, smooth or notsmooth for the distal humerus, in particular the capitulum implantand/or for the proximal radius. In particular, special anchoring devicesof the implants such as, e.g., shafts of different shapes, wedges orhooks may have the described surfaces.

Some or all embodiments according to the present invention may compriseone, several or all of the advantages mentioned above and/or in thefollowing.

The joint replacement is characterized through the most congruence withthe native form of the capitulum. The different curvature radii of thejoint surface are advantageously imitated (at least two different radii)on the joint replacement. Due to the shape of the adjacent joint surfaceat the radius and the form at the distal humerus (direction trochlea),it is also advantageous if the joint surface terminates medially with acollar section. On the lateral side, the shape may be determineddistally by the taper by an angle. The transfer of this angle to theimplant shape may have a positive effect on the adjacent ligaments. Anincreased biomechanical stability may be achieved by the shape anddimensions of the implant. Ligaments are preserved during implantationby the possibility of soft tissue-protecting and/or minimally invasiveinsertion and by the position and dimensions.

The present invention is exemplarily described in the following based onthe accompanied figures in which identical reference numerals refer tothe same or similar components. In each of the schematically simplifiedfigure, the following applies:

FIG. 1a-e show a capitulum implant of a partial elbow joint replacementin a first exemplary embodiment;

FIG. 2 shows the morphology of bone structures of a distal humerusregion;

FIG. 3a-d show a capitulum implant of a partial elbow joint replacementaccording to the present invention which is virtually implanted on acapitulum of a distal humerus region;

FIG. 4a-b show a capitulum implant of a partial elbow joint replacementaccording to the present invention in a second exemplary embodiment;

FIG. 5a-c show a capitulum implant of a partial elbow joint replacementaccording to the present invention in a third exemplary embodiment;

FIG. 6a-c show a capitulum implant of a partial elbow joint replacementaccording to the present invention in a fourth exemplary embodiment;

FIG. 7a-c show a capitulum implant of a partial elbow joint replacementaccording to the present invention in a fifth exemplary embodiment;

FIG. 8a-b show a capitulum implant of a partial elbow joint replacementaccording to the present invention in a sixth exemplary embodiment;

FIG. 9a-c show a capitulum implant of a partial elbow joint replacementaccording to the present invention in a seventh exemplary embodiment;

FIG. 10a-b show a capitulum implant of a partial elbow joint replacementaccording to the present invention in an eighth exemplary embodiment;

FIG. 11a-b show a capitulum implant of a partial elbow joint replacementaccording to the present invention having a conical shaft as ananchoring device;

FIG. 12a-c show a capitulum implant of a partial elbow joint replacementaccording to the present invention having a trapezoidal shaft as ananchoring device;

FIG. 13a-c show a capitulum implant of a partial elbow joint replacementaccording to the present invention having a wedge as an anchoringdevice;

FIG. 14a-c show a capitulum implant of a partial elbow joint replacementaccording to the present invention having a barb as an anchoring device;

FIG. 15a-c show a capitulum implant of a partial elbow joint replacementaccording to the present invention having a flap for fixing screws as ananchoring device;

FIG. 16a-b show a capitulum implant of a partial elbow joint replacementaccording to the present invention having a flap for fixing screws whichis fixed by a hinge as an anchoring device;

FIG. 17a-b show a radial head implant of a partial elbow jointreplacement according to the present invention

FIG. 18a-b show a radial head implant with a wedge-formed mandrel as ananchoring device of an elbow joint replacement according to the presentinvention

FIG. 19a-c show a radial head implant with a wedge as an anchoringdevice of an elbow joint replacement according to the present invention;

FIG. 20a-b show a radial head implant with a further wedge as ananchoring device of an elbow joint replacement according to the presentinvention;

FIG. 21a-c show a radial head implant with a further wedge as ananchoring device of an elbow joint replacement according to the presentinvention;

FIG. 22a-c show schematically the individual steps for introducing aradial head implant into the proximal radius;

FIG. 23 shows the insertion of a K-wire into the distal humerus forpreparing the implantation of a partial elbow joint replacementaccording to the present invention;

FIG. 24 shows a milling head with a tissue protector for machining orremoving of bone structures;

FIG. 25 shows the K-wire inserted into the milling head with a tissueprotector while machining or removing of bone structures; and

FIG. 26a-f show different views of the partial elbow joint replacementaccording to the present invention with a capitulum implant as ashell-like segment and a radial head implant.

FIG. 1a shows a perspective view of a first exemplary embodiment of acapitulum implant 100 of a partial elbow joint replacement 1000 for anelbow joint. The exact arrangement of the capitulum implant 100 assurface replacement of the capitulum humeri at the lateral section ofthe distal humerus is illustrated in the FIGS. 3a to 3d and is describedwith respect thereto.

The capitulum implant 100 is in the following referred to as implant 100in a simplified way.

The capitulum implant 100 may be designated as a shell-like segment 100.

The implant 100 is shell-like shaped and has a curved outer surfacecontour 1 (outer contour) and an inner surface contour (inner contour)3. The implant 100 is optionally not closed neither on a lateral endface 5 nor on a medial end face 7 thereof.

The thickness of the wall of the implant 100, i.e. the distance betweenthe outer surface and inner surface of the implant 100, is in this firstembodiment constant through all the sections of the implant 100.

In the circumferential direction u (see FIG. 1c ), the shell-like formis optionally also not closed, as this is described in more detail inthe following figures.

The longitudinal direction of the implant 100 is denoted with x.

FIG. 1b shows the implant 100 of FIG. 1a in a side-view in which aninflection point 9 is visible in the outer surface seen in longitudinaldirection x. At this point the inflection point 9 is the transitionpoint between the approximately spherical shape in the region of thecapitulum humeri (on the lateral side of the implant) and the mediallyadjoining region of the implant 100 in the direction of the trochleahumeri (see FIGS. 2 and 3).

The inner contour 3 of the implant 100 is approximately anatomicallyformed, corresponding to the natural joint surface, so that as littlebone substance as possible has to be removed or milled off before theimplant 100 is implanted. This allows an improved blood circulation ofthe bone compared to procedures where more bone substance is removed.

Further, the view in FIG. 1b shows that the medial end face 7 closes orterminates perpendicular to the longitudinal direction x by way ofexample, whereas the lateral end face 5 closes with a curve-form, whichis described in more detail in the following figures.

FIG. 1c shows a further perspective view of the implant 100 of FIG. 1aobliquely from the top on the curved outer surface 1 and the medial endface 5.

FIG. 1d shows the implant 100 of FIG. 1a in a side view in which theimplant 100 relative to the view in FIG. 1b is tilted by 180 degreesabout a transvers axis (in radial direction r) and rotated by 90 degreesabout its longitudinal axis x. The medial end face 7 is arranged on theleft, the lateral end face 5 on the right.

In this view, the form of the lateral end face 5 is clearly visible.This form is adapted to the lateral, anatomical end of the capitulumhumeri (see FIGS. 2 and 3).

Together with the view in FIG. 1e , individual exemplary dimensions arespecified for the dimensioning of different implant sizes. Theseexemplary dimensions result from the measurements or determinationscarried out by computer tomography (CT images) of about 30 patient datasets of distal humeri.

FIG. 1e shows a view of the implant 100 of FIG. 1d tilted by 90 degreesaround the radial axis r to the left and rotated around the longitudinalaxis x

The parameters measured or determined by means of the patient data arecategorized in the following exemplary implant sizes. The abbreviationsfor the implant sizes are as follows:

S—Small; M—Medium; L—Large; XL—Extra Large

S M L XL X₁ [mm] 17.65 20.15 22.65 25.15 X₂ [mm] 10.18 11.51 12.85 14.19X₃ [mm] 6.38 7.34 8.30 9.27 R₁ [mm] 8.60 9.80 11.00 12.20 R₂ [mm] 7.087.89 8.70 9.51 R₃ [mm] 7.63 8.58 9.52 10.47 R₄ [mm] 10.78 11.59 12.3913.20 R₅ [mm] 3.93 4.06 4.18 4.31 α [degree; °] 35 35 35 35 ß₁ [degree;°] 120 120 120 120 ß₂ [degree; °] 80 80 80 80

FIG. 2 shows the morphology of bone structures of a distal humerusregion. Shown are in particular the elbow joint 11 (or the portions ofthe humerus thereon) with the capitulum 13 and the trochlea 15, whichbuild the distal end region of the humerus 17. For example, if the elbowjoint is damaged or injured in the region of the capitulum 13, thesurface of the capitulum 13 can be replaced by a partial elbow jointreplacement 1000 according to the present invention as shown in FIGS. 3ato 3d , for instance after milling of surface layers of bone structures.

FIG. 3a shows a capitulum implant 100 of a partial elbow jointreplacement 1000 according to the present invention which is virtuallyimplanted on the capitulum of a distal humerus region. The markedcutting or intersecting planes M1, M2 and IK are e.g. measurement planeswhich refer to characteristic planes in the imaging examinations of thepatient. The measuring results may provide indications for the surgeonconcerning the size of the implant 100 to be selected for implanting apartial elbow joint replacement 1000 (see description to FIG. 1, implantsizes: S/M/L/XL). The longitudinal direction x may be referred to asrotation axis. The rotation axis may be related to the implant 100 aswell as to the trochlea and/or capitulum. The marked cutting planes M1,M2 and IK are arranged perpendicular (or orthogonal) to the rotationaxis.

FIG. 3b shows a prototype of the implant 100, placed on a model of adistal humerus made of plastic, and an elbow joint. The implant 100 isplaced on the capitulum 13 of the distal humerus 17. In this view it iseasy to see how the lateral end region 5 and the medial end region 7 ofthe implant 100 adapt themselves to the adjacent bone structures orattach to them.

FIG. 3c shows the view of FIG. 3b rotated or tilted by 90 degrees to theright. The circumferential angle around the rotation axis or thelongitudinal axis x is larger than 180 degrees, analogous to FIG. 1e ,in which the circumferential angle measures 200 degrees (β₁: 120degree+β₂: 80 degrees), so that the implant 100 to be placed on thecapitulum 13 must be slightly expanded before it can be attached to thecapitulum 13 in a form-closure manner.

FIG. 3d shows a virtual arrangement of the implant on the capitulum 13.Shown in this view are the parallel axes of a longitudinal axis 19 ofthe humerus 17, in which the longitudinal axis is in particular theshaft axis 19 of the humerus 17, and an axis in radial direction r ofthe implant 100, which is at the same time a radial direction r of thecapitulum. The radial direction r is perpendicular or orthogonal to therotation axis, or to the longitudinal axis x, of the implant 100.

FIG. 4a shows a capitulum implant 100 of an elbow joint replacementaccording to the present invention 1000 in a second exemplarilyembodiment. Compared to the form and contour of the first embodiment ofthe implant 100 from FIGS. 1a to 1c , the second embodiment comprises acylindrical inner contour 21 in the medial end section 7. A cylindricalinner contour 21 may simplify a processing of the bone structure, e.g.by using a suitable cutting miller, compared to a continuouslyanatomically formed contour (see FIGS. 1a to 1c ). An anatomicallyformed contour may imply a greater effort and a longer processing time,also of the corresponding bone structures, due to concave contours andto possible freeform surfaces.

A securing against a translational displacement of the implant 100 alongthe x-direction after a positioning on the capitulum 13 may be achievedby the remaining shape of the concave inner contour (lateral side). Thesecuring is thus independent of the inner contour shape in the medialend region 7. However, an anatomical shape (see FIGS. 1a to 1c ) mayadvantageously additionally block and protect against a displacementalong the x-direction.

The wall thickness of the implant 100 may in the area of the cylindricalinner contour 21 be greater and may possibly comprise an increasedstability against an anatomically formed inner contour—at least insections of the inner contour.

A lateral sliding of the implant 100 of the second embodiment withregard to FIG. 4a and FIG. 4b (in FIG. 4a from left to right) onto thecapitulum 13 may be made easier or even possible for the first time dueto the cylindrical inner contour 21, compared to the anatomical shapeaccording to FIGS. 1a to 1c . Due to the undercut in the medial endregion 7, the anatomical shape may prevent or at least hinder a lateralsliding.

An anatomically-shaped inner contour (see FIG. 1a to FIG. 1c ) mayreduce and minimize the amount of a necessary bone resection (removal ofbone structures for adaptation to the implant shape) compared to thecylindrical inner contour 21.

FIG. 4b shows a perspective view of the second embodiment of the implant100.

FIG. 5a shows a capitulum implant 100 of an elbow joint replacement 1000according to the present invention in a third exemplary embodiment. Inthis third embodiment, the inner contour 3 (or inner surface form) iscontinuously, i.e. from medial 7 end region to lateral end region 5,cylindrical.

A cylindrical inner contour may simplify and facilitate the processingof the bone structure on which the implant 100 is placed. A cylindricalshape is usually easier to achieve, for example by milling, than ananatomical contour as shown in FIG. 1a to FIG. 1c . However, anincreased volume of removed bone structures may be undesirable for otherreasons (for example an increased bone stability as the basis for thestability of the implant 100). Therefore, minimum internal radii maypurely exemplarily be given for the cylindrical inner contour whichrefer to the table in FIG. 1e with respect to the other dimensions (seeabove). These minimum internal radii are intended to ensure a sufficientbone substance for fixing and stabilizing the implant 100. The valuesgiven in the following are to be understood purely as an example. Forthe implant category S (Small), a minimum internal radius of 5.4 mm canbe given, for M (Medium): 6.0 mm, for L (Large): 6.6 mm and for XL(Extra Large): 7.2 mm. Thus, the wall thicknesses of the implant, inparticular in the stressed area (through natural arm movements and theresulting forces on the elbow joint), are approximately between 3.2 mm(for S) and 5 mm (for XL).

A cylindrical inner contour may simplify or even allow lateral slidingof the implant 100 on the capitulum 13, in particular at acircumferential angle β being greater than 180 degrees (see FIG. 1e ).

However, a cylindrical inner contour may not ensure or may less reliablyensure securing and/or anchoring against translational movements alongthe axis of rotation (longitudinal axis x) as well as a rotation of theimplant 100 and the axis of rotation (in circumferential direction u)without additional fixations using screws, or anchoring the implant 100.

FIG. 5b shows a side view and FIG. 5c shows a perspective view of thethird exemplary embodiment of the implant 100. FIG. 5b clearlyillustrates that the circumferential angle β (see the description ofFIG. 1e ) is greater than 180 degrees.

FIG. 6a shows a capitulum implant 100 of an elbow joint replacement 1000according to the present invention in a fourth exemplary embodiment.Compared to the third embodiment, the fourth embodiment comprises acylindrical landing 23 shifted to the inside and arranged in thecircumferential direction u. The shifted cylindrical landing 23 may bereferred to as a section having a cylindrical step having a smallerradius compared to the cylindrical form arranged further laterally. Thedescriptions and discussions related to FIG. 5a apply largelyanalogously to FIG. 6a . However, the implant 100 of the fourthembodiment may not be shifted laterally in the longitudinal direction xonto the capitulum 13, but must be placed from the front (anterior). Forthis reason, it is necessary that the circumferential angle β (see FIG.1e ) is max. 180 degrees. After placement on the capitulum 13, theimplant 100 is secured against displacement (translational movement in xdirection) on the capitulum 13 of the elbow joint.

FIG. 6b shows a side view rotated approximately 90 degrees around thelongitudinal axis x, and FIG. 6c shows a perspective view of the fourthexemplary embodiment of the implant 100.

FIG. 7a shows a capitulum implant of a partial elbow joint replacement1000 according to the present invention in a fifth exemplary embodiment.This embodiment is very similar to the fourth embodiment (FIG. 6),wherefore the description and discussion related to FIG. 6 applyanalogously also here. Only the cylindrical landing 23 of FIG. 6a whichis shifted to the inside is embodied in FIG. 7a in a semicircular shape.The step which arranged to the inside may be referred to as semicircularnotch 25. This exemplarily has an effect on the form of the processingof bone structure in this region and requires a modified manufacturingof the implant 100.

The notch 25 may alternatively to the semicircular shape compriseanother form.

FIG. 7b shows a side view rotated approximately 90 degrees around thelongitudinal axis x and FIG. 7c shows a perspective view of the fifthexemplary embodiment of the implant 100.

FIG. 8a shows a capitulum implant 100 of a partial elbow jointreplacement 1000 according to the present invention in a perspectiveview in a sixth exemplary embodiment. Compared to the fourth embodiment(FIG. 6) and fifth embodiment (FIG. 7), the sixth embodiment comprisesin the longitudinal direction x two notches 27 which are arranged on theopposite circumference, shifted to the inside and semicircular. Thenotches 27 are respectively arranged on both end sections of implant 100which are not closed in the circumferential direction u. In particular,FIG. 8b clearly illustrates that the circumferential angle β is greaterthan 180 degrees, so that the implant can either be shifted on thelateral side of the capitulum 13 or placed on the radial side by(elastically) spreading apart the implant 100.

The notch 27 may alternatively to the semicircular shape compriseanother form.

FIG. 8b shows the medial end face side of the implant 100.

FIG. 9a shows a capitulum implant 100 of a partial elbow jointreplacement 1000 according to the present invention in a seventhexemplary embodiment. Compared to the third embodiment (FIG. 5), theinner contour (or inner surface shape 3) is continuously flat shaped,from the medial end section 7 to the lateral end section 5. Thisflat-shaped surface may prevent a rotation of the implant 100 afterplacing it on the capitulum 13. The implant 100 is secured against arotation around the longitudinal axis x. Prior to implantation, the bonestructure of the capitulum 13 may be processed and sawn laterally, forexample, with the aid of a saw template. Subsequently, the implant 100may be shifted laterally.

FIG. 9b shows a lateral view of the end face of the implant 100 and FIG.9c shows a perspective view thereof.

FIG. 10a shows a capitulum implant 100 of a partial elbow jointreplacement 1000 according to the present invention in an eighthexemplary embodiment. Compared to the embodiment of FIG. 9a , the innercontour 3 comprises additional surfaces and has a trapezoidal design inthe cross section or in a section perpendicular to the longitudinal axisx. The inner contour 3 may comprise two, three or more surfaces.

FIG. 10b shows a medial view of the end face of the implant 100.

FIG. 11a shows a capitulum implant 100 of a partial elbow jointreplacement 1000 according to the present invention having a conicalshaft 29 as an anchoring device.

The anchoring mechanisms illustrated in FIGS. 11 to 16 may be combinedwith the illustrated and described embodiments of the inner contour(FIGS. 1, 4, 5, 6, 7, 8, 9, 10). The anchoring mechanisms may beoptionally rounded respectively at corners and edges and/or the surfaces(of the respective anchoring mechanism) may be optimized through theirsurface roughness and/or through an optional coating forosteointegration.

All the anchoring mechanisms illustrated in FIGS. 11 to 16 may prevent atranslational movement in the x direction and/or a rotational movementaround the longitudinal axis of the implant 100.

The bone structures may be prepared for the anchoring mechanismsillustrated in FIGS. 11 to 16, for example by a reamer, a rasp and/or asaw or the like. The respective anchoring mechanism may be pressed intothe capitulum or generally into the bone substance by a so-calledpress-fit. This may improve or accelerate the osteointegration of theimplant 100.

In the anchoring mechanism, undercuts may be provided into which thebone structure can grow and thus increase a long-term stability of theimplant 100.

The position of the respective anchoring mechanism is arranged andprovided, in particular at the maximum radius of the capitulum and/or atthe largest radius of the implant. The exact position and/or the angleat which the respective anchoring mechanism is inserted into the bonestructure may vary on the patient depending on the intraoperativesituation.

FIG. 11b shows a lateral view of the end face of the implant 100 havingthe conical shaft 29.

FIG. 12a , FIG. 12b and FIG. 12c show a capitulum implant 100 of apartial elbow joint replacement 1000 according to the present inventionhaving a trapezoidal shaft 31 as an anchoring device.

FIG. 13a , FIG. 13b and FIG. 13c show a capitulum implant 100 of apartial elbow joint replacement 1000 according to the present inventionhaving a wedge 33 as an anchoring device.

The wedge 33 extends in particular parallel to the axis of the rotationx of the implant 100 and of the elbow joint. The wedge 33 may have aso-called sawtooth profile, which can prevent a lateral displacement ofthe implant 100.

For inserting the implant 100 with the wedge 33 as an anchoring deviceinto the bone, a notch may be sawn into the bone for bone preparation.The implant 100 may thereby be pushed from lateral side withoutspreading the bone apart of the elbow joint.

FIG. 14a , FIG. 14b and FIG. 14c show a capitulum implant 100 of apartial elbow joint replacement 1000 according to the present inventionhaving a barb 35 as an anchoring device.

The barbs 35 are arranged on the inside of the implant 100. As shown inFIG. 14, the barbs 35 may be angular or alternatively conical. Theradial expansion or height may be limited to 3 mm by way of example.

The implant 100 may advantageously be inserted into the bone withoutfurther pretreatment. A pre-drilling or the like is not necessarybecause of the small size of the barbs 35.

The barbs 35 may lead to or effect a primary stability of the implant100 against translation (in longitudinal direction x) and/or against arotation (around the longitudinal axis x).

The barbs 35 may alternatively or additionally arranged laterally at theedges in the circumferential direction 37 and/or only laterally ormedially.

FIG. 15a , FIG. 15b and FIG. 15c show a capitulum implant 100 of apartial elbow joint replacement 1000 according to the present inventionhaving a flap for fixing screws 39 as an anchoring device. The flap 39may be referred to as a lug.

The flap 39 is laterally arranged at the end face of the implant 100.The flap comprises an opening 41 or bore which is arranged at the heightof the rotation axis x. Through the opening 41, a screw may beintroduced into the bone. This maintains and fixes the implant 100 inits position. The diameter of the screw may be purely exemplarily appr.2 mm. When fixing or anchoring the implant 100 using the element 39 anda screw is introduced by the opening 41, there is particularly nofurther preparation, e.g. a predrilling of the bone, needed.

For implantation, the implant 100 can be guided, e.g. using the opening41, through a guide wire, which is also used for processing (usingmilling and sawing) of the bone structure of the capitulum and/or of theelbow joint, and pushed onto the capitulum. The guide wire cansubsequently be removed and the screw for fixing the implant can beinserted.

FIG. 16a and FIG. 16b show a capitulum implant 100 of a partial elbowjoint replacement 1000 according to the present invention having a flap39′ for fixing screws as an anchoring device.

The flap 39′ is fixed by a hinge 43.

The flap 39′ is attached to the implant 100 by the hinge 43. Due to therotatability of the flap 39′ relative to the implant 100 on the basis ofthe hinge 43 the implant 100 and the flap 39′ may advantageously beadapted and optimized to the anatomical situation of the capitulum.

Optionally, the flap 39′ may only be used for the guided application ofthe implant 100 to the implantation position on the capitulum, in orderto decouple and remove the flap 39′ after positioning the implant 100.For example, depending on the situation during implantation, anotheranchoring mechanism could be selected or, due to the inner contour, nofurther anchoring mechanism might be necessary.

FIG. 17a shows a radial head implant 200 of an elbow joint replacement1000 according to the present invention.

The radial head implant 200 is provided for replacing the radial head(proximal, elbow-close). The aim of an implantation of a radial headimplant 200 is to at least partially restore the articular mechanism,for example as a result of an arthrosis or after a traumatic event suchas an accident. In particular, the sizes and proportions of the radialhead implant 200 according to the present invention are based on ananatomical analysis.

The radial head implant 200 comprises a recess depth 45 which is adapted(varies with the implant sizes S/M/L/XL; see table according to FIG. 1e) to the radius (see table according to FIG. 1e , e.g. R₄) and to theheight of the capitulum implant 100. The outer wall 47 of the radialhead implant 200 is curved so that the radial head implant fits into thearticular surface of the ulna (the lower arm bone encompasses theso-called spine or radius and the so-called ell or ulna, which togetherwith the capitulum and the trochlea substantially form the elbow joint).

The radial head implant 200 may be made of one or more biocompatiblematerials, such as e.g. metal, ceramic, plastic, composite and/or acombination thereof. Examples of biocompatible materials are the metalalloy cobalt chromium molybdenum, the ceramics zirconium oxide, aluminaoxide (Al₂O₃) or the plastics polyetheretherketone (PEEK), ultrahighmolecular weight polyethylene (UHMWPE). Purely exemplarily, slide orglide pairings with the capitulum implant 100 and the radial headimplant 200 could be a metal-plastic or ceramic-ceramic pairing. Theseslide pairings are known as low-abrasion material pairings and maytherefore be advantageously used as a permanent pair of materials.Furthermore, such material pairings may be associated with a low risk ofinfection and/or with the avoidance of allergic reactions.

FIG. 17b shows a side view of the radial head implant 200.

FIG. 18a-b show a radial head implant 200 having a wedge-shaped shaft 49as an anchoring device.

The wedge-shaped shaft 49 may, like the below-described anchoringdevices (see FIG. 19, 20, 21) be coated. A coating may improve or atleast positively influence a so-called osteointegration (bone ingrowthor bone growth). A coating may, for example, comprise pure titanium,which is applied in a so-called plasma spray process with a layerthickness of approximately 40-50 μm and a roughness of approximately 7μm. Alternatively, a coating may comprise hydroxyapatite, referred to asa so-called bone cement. Other coating materials and methods are alsopossible.

The wedge-shaped shaft 49 in FIGS. 18a and 18b comprise a rounded tipwhich may counteract additional or further damage to the bone duringimplantation. The lateral notches 51 of the wedge-shaped shaft 49 mayfavor or promote osteointegration. Furthermore, lateral notches 51 mayincrease the stability of the radial head implant 200, for exampleagainst a rotation around the longitudinal axis. The lateral notches 51may be referred to as undercuts.

FIG. 19a , FIG. 19b and FIG. 19c show a radial head implant 200according to the present invention having a wedge-shaped mandrel 53 asan anchoring device.

The wedge-shaped mandrels 53 may be referred to as flexible spikes whichadapt to the respective surface when they are inserted into the bone (ormedullary space). The mandrels 53 may be bent to the inside after beinginserted in order to provide stability by tension in the mandrels 53which are pressing against the bone. Optionally, the mandrels 53 mayhave barbs at the tip which “bury” themselves into the bone, therebyproviding additional securing against slipping and/or rotation.

FIG. 20a and FIG. 20b show a further radial head implant 200 accordingto the present invention having a short wedge 55 as an anchoring device.

The stability of the radial head implant 200 may be achievedpredominantly by positioning and resting the head (upper part) of theradial head implant 200 on the cortical portion of the radial neck. Theshort wedge 55 may be inserted into the medullary space, or if there isstill spongy bone present, into this region. Due to the little height ofthe wedge, a wide spreading of the joint line, of the bone or of themedullary space may be avoided. In this way, for example, soft tissueand/or ligaments may be protected and the natural joint stability may bemaintained. The openings 57 may improve the ingrowth of the bone intothe wedge 55 and thus allow a long-term stability of the implant 200.

FIG. 21a , FIG. 21b and FIG. 21c show a further radial head implant 200according to the present invention having a T-shaped wedge 59 as ananchoring device.

The T-shape of the wedge 59 allow a generally high stability of theradial head implant 200 and generally permits a larger design spectrumof the radial head implant 200. The lateral side of the wedge 59 (in theupper region in FIGS. 21b and 21c ) is rounded to the inside, whereby awide spreading of the intra-articular space, of the bone or of themedullary space may be avoided.

The medial side of the wedge 59 (the lower region in FIGS. 21 and 21 c)is wide and rounded so that the largest possible contact area with thebone can be created. The tip of the wedge 59 is rounded so that cuttinginto the bone may be avoided when the radial head implant 200 isinserted and the bone is not additionally damaged. The wedge 59comprises a plateau toward the head so that the wedge can be supportedon both sides by the bone. The wedge 59 can have a height ofapproximately 15 mm purely by way of example.

FIG. 22a , FIG. 22b and FIG. 22c show schematically the individual stepsfor introducing a radial head implant 200 into the medullary space 63 ofthe proximal radius 61. The position of the natural, already removed,radial head is shown in dashed lines.

The joint line 65 between the capitulum 13 and the proximal radius 61may e.g. be already widened by removed bone material on the capitulum 13or through atraumatic spreading apart, e.g. up to about 5 mm, so thatthe radial head implant 200 can be introduced, as shown in FIGS. 22a to22 c.

FIG. 23 shows the introduction of a K-wire 67 into the distal humerus 17for preparing the implantation of a capitulum implant 100 according tothe present invention. The K-wire 67, which comprises a diameter ofapproximately 2 mm, purely by way of example, is guided laterally (inFIG. 23 from the left) via the rotation axis x first into the capitulumand then into the trochlea. The rotation axis x is the natural rotationaxis of the illustrated joint.

The K-wire 67 may be referred to as drill wire 67.

FIG. 24 shows a milling head 69 having a tissue protector 71 for themachined removal of bone structures. The form of the milling head 69(the milling head 69 may be referred to as a shaver) shows an almostanatomical shape in order to remove as little as possible of bonematerial from the surface. Alternatively the milling head 69 maycomprise a simplified form of a barrel or container or a parabolic form.The tissue protector 71 remains unmoved during the milling process. Themilling head 69 rotates about its own rotation axis and removes bonematerial in this way.

FIG. 25 shows the milling head 69 which was pushed on the K-wire 67 andthe tissue protector 71 during removal of bone structures.

FIG. 26a-f show different views of the partial elbow joint replacement1000 according to the present invention having a capitulum implant as ashell-like segment 100 and a radial head implant 200.

LIST OF REFERENCE NUMERALS

-   1000 partial elbow joint replacement-   100 capitulum implant; implant (part of a partial elbow joint    replacement); shell-like segment-   200 radius head implant (part of a partial elbow joint replacement)-   x x-direction, longitudinal direction, longitudinal axis-   r radial direction, direction perpendicular to the longitudinal    direction-   u circumferential direction-   X1 length of the partial elbow joint replacement-   X2 distance in x-direction of the implant from the medial end to the    longitudinal position having the maximum radius of the implant-   X3 distance in x-direction of the implant from the longitudinal    position having the smallest radius between capitulum and trochlea    and the longitudinal position with the maximum radius of the implant-   R1 maximum radius of the implant perpendicular to the longitudinal    direction-   R2 smallest radius of the implant between capitulum and trochlea    perpendicular to the longitudinal direction-   R3 outer radius on the medial end face of the implant perpendicular    to the longitudinal direction-   R4 radius of the capitulum surface of the implant-   R5 radius of the implant surface in the longitudinal direction    between capitulum and trochlea-   α angle to the radial direction-   β1, β2 circumferential angle-   1 outer surface shape, outer contour-   3 inner surface shape, inner contour-   5 lateral end; lateral end region; lateral end face; lateral section-   7 medial end; medial end region; medial section-   9 inflection point-   11 elbow joint-   13 capitulum-   15 trochlea-   17 humerus; distal humerus-   19 longitudinal axis of the humerus; shaft axis of the humerus-   21 cylindrical inner contour-   23 cylindrical landing-   25 notch in the circumferential direction u-   27 notch in the longitudinal direction x-   29 conical shaft (as anchoring device)-   31 trapezoidal shaft (as anchoring device)-   33 wedge (as anchoring device)-   35 barb-   37 edge (in circumferential direction)-   39, 39′ flap for fixing or fastening screws-   41, 41′ opening, bore-   43 hinge-   45 depth of recess-   47 external wall of the radial head implant-   49 wedge-shaped shaft-   51 lateral notch-   53 wedge-shaped mandrel-   55 short wedge-   57 opening (in the short wedge)-   59 T-shaped wedge-   61 proximal radius-   63 medullary-   65 joint line-   67 K-wire; Kirschner wire-   69 milling head-   71 tissue protector

1. A partial elbow joint replacement (1000) comprising: a shell-likesegment (100) along a longitudinal direction (x) with a concave innercontour (3) for its arrangement on or at bone structures of a patient,wherein the segment (100) comprises a lateral section (5) and a medialsection (7); and wherein an outer contour (1) of the segment (100)comprises at least one inflection point (9) in the longitudinaldirection (x).
 2. The partial elbow joint replacement (1000) accordingto claim 1, wherein the extension of the lateral section (5) in radialdirection (r) is larger than the extension of the medial section (7) inradial direction (r).
 3. The partial elbow joint replacement (1000)according to claim 1, wherein the shell-like segment (100) comprises noclosed circumference in circumferential direction (u) which isperpendicular to the longitudinal direction (x) and/or perpendicular tothe radial direction (r).
 4. The partial elbow joint replacement (1000)according to claim 1, wherein the shell-like segment (100) comprises awall thickness between 1 mm and 5 mm, in particular between 2 mm and 3mm.
 5. The partial elbow joint replacement (1000) according to claim 1,wherein the outer contour (1), at least in sections, has been adapted ina preoperative planning stage to be patient-specific by means of acomputer imaging, in particular such that it conforms to a correspondingbone part of an elbow joint of the patient.
 6. The partial elbow jointreplacement (1000) according to claim 1, wherein the shell-like segment(100) comprises a rough inner contour surface (3).
 7. The partial elbowjoint replacement (1000) according to claim 1, wherein the inner contour(3) of the segment (100) is designed, in the longitudinal direction (x),in an analogous manner the outer contour (1) of the segment (100). 8.The partial elbow joint replacement (1000) according to claim 1, whereinthe inner contour (3) of the segment (100) comprises in longitudinaldirection (x) at least one inflection point (9).
 9. The partial elbowjoint replacement (1000) according to claim 1, wherein the inner contour(3) of the lateral section of the segment (100) comprises a concave,non-cylindrical contour, and wherein the inner contour (3) of the medialsection of the segment (100) comprises a cylindrical contour inlongitudinal direction (x).
 10. The partial elbow joint replacement(1000) according to claim 1, wherein the inner contour (3) of thelateral section of the segment (100) comprises a concave,non-cylindrical contour, and wherein the inner contour (3) of the medialsection of the segment (100) comprises a convex contour in longitudinaldirection (x) which is radially bent to the inside.
 11. The partialelbow joint replacement (1000) according to claim 1, wherein the innercontour (3) of the lateral section of the segment (100) comprises aconcave, non-cylindrical contour, and wherein the inner contour (3) ofthe medial section of the segment (100) comprises a convex contour inthe circumferential direction (u) which is radially bent to the inside.12. The partial elbow joint replacement (1000) according to claim 1,wherein the inner contour (3) of the lateral section of the segment(100) comprises a cylindrical contour, and wherein the inner contour (3)of the medial section of the segment (100) comprises a convex contour inlongitudinal direction (x) or a convex contour in circumferentialdirection (u).
 13. The partial elbow joint replacement (1000) accordingto claim 1, wherein the shell-like segment (100) comprises at itslateral end section at the end face a fixing unit for fixing theshell-like segment (100) to the bone.
 14. The partial elbow jointreplacement (1000) according to claim 13, wherein the fixing unitencompasses a screw.
 15. The partial elbow joint replacement (1000)according to claim 13, which is fixable in the bone parallel to thelongitudinal direction (x) by the fixing unit.
 16. The partial elbowjoint replacement (1000) according to claim 1, wherein the segment (100)comprises at its inner side (3) at least one anchoring device foranchoring the segment (100) in a bone structure.
 17. The partial elbowjoint replacement (1000) according to claim 1, wherein the longitudinaldirection (x) extends parallel to a rotation axis of the elbow joint,the longitudinal direction (x) is in the implanted state of the elbowjoint replacement (1000) a rotation axis of the elbow joint and/or thelongitudinal direction (x) is an epicondyle axis of the elbow joint. 18.The partial elbow joint replacement (1000) according to claim 1, whereinthe inner side (3) of the segment (100) is shaped such that it conformsto a surface of a proximal ulna of the elbow joint.
 19. The partialelbow joint replacement (1000) according to claim 1, wherein the segment(100) has at its lateral end an inlet or opening plane or wall whichlies in a plane being under an angle (α) relative to the longitudinaldirection (x).
 20. The partial elbow joint replacement (1000) accordingto claim 1, wherein the angle (α) has a value within a range of 25° to45°, preferably between 30° and 40°, more particularly preferred is 35°.